<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>边框</title>
		<style type="text/css">
			.c1{
				height: 400px;
				width: 400px;
				border: 1px  red solid;
				margin:0 0 5px;
				padding: 30px;
			}
			#d2{
				box-sizing: border-box;
			}
		</style>
	</head>
	<body>
		<div class="c1" id="d2">aaa</div>
		
		<div class="c1">bbb</div>
	</body>
</html>